1. Field of the Invention
The present invention relates to a so-called front-opening interface mechanical standard (FIMS) system used when wafers held in a transfer container which is called a pod are transferred among semiconductor processing apparatuses in a semiconductor manufacture process or the like. More specifically, the present invention relates to a detecting device for detecting the states of wafers in the FIMS system in which a pod containing the wafers which is called a front-opening unified pod (FOUP) is placed and the wafers are moved using the pod.
2. Related Background Art
Up to now, a semiconductor manufacture process has been conducted in a so-called clean room in which a room in which semiconductor wafers are treated has high cleanliness. However, in order to increase the wafer size and reduce the cost required to maintain the room clean, a method of maintaining the inner portion of a processing apparatus, the pod (wafer container), and a mini-environment for substrate transfer from the pod to the processing apparatus with a high cleanliness state has been employed in recent years.
The pod includes a main body portion having a substantially cube shape and a lid. The main body portion includes a rack capable of holding a plurality of wafers therein with a state in which the wafers are separated from one another in parallel and an opening portion which is provided on a surface of the rack and is used for wafer transfer. The opening portion is closed with the lid. A pod in which a forming surface of the opening portion is located not vertically below the pod but on a side surface of the pod (in front of the mini-environment) is generically called a front-opening unified pod (FOUP). The present invention is mainly for a structure using the FOUP.
The above-mentioned mini-environment includes a first opening portion opposed to the opening portion of the pod, a door for closing the first opening portion, a second opening portion provided on a semiconductor processing apparatus side, and a movable robot that moves from the first opening portion to the inner portion of the pod to hold the wafer and passes through the second opening portion to transfer the wafer to the semiconductor processing apparatus side. The structure for forming the mini-environment includes a mount base for supporting the pod so that the opening portion of the pod is simultaneously opposed to the front surface of the door.
A positioning pin inserted into a positioning hole provided on a lower surface of the pod to regulate a mount position of the pod and a clamp unit engaged with a portion to be clamped which is provided on the lower surface of the pod to hold the pod to the mount base are located on an upper surface of the mount base. The mount base is normally movable in a door direction by a predetermined distance. When the wafers in the pod are to be transferred to the processing apparatus, the pot is moved in a state in which the pod is mounted until the lid of the pod comes in contact with the door. After that contact, the pod is opened by the door and the lid is removed. Therefore, the inner portion of the pod is connected to the inner portion of the processing apparatus through the mini-environment. Subsequently, wafer transfer operation is repeated. A system including the mount base, the door, the first opening portion, a door open-and-close mechanism, and a wall which is a part of the mini-environment including the first opening portion is generally called a front-opening interface mechanical standard (FIMS) system.
When the operation for closing the pod with the lid is to be performed, it is necessary to store all the wafers in the pod at predetermined positions as a precondition. However, for example, there may be a case where one of the wafers is not accurately placed on the rack of the pod from some causes and thus a part of the wafer exists out of the opening portion of the pod. When the normal lid-close operation is performed in such a situation, it is likely to cause a large process problem such as a damage to the wafer. Therefore, normally, a sensor for detecting the slip-out of a wafer from the pod is provided to detect such a situation, thereby preventing, for example, the damage to the wafer. Examples of such a detection device are disclosed in Japanese Patent Application Laid-open No. 2003-273197, Japanese Patent Application Laid-open No. 2003-100852, and Japanese Patent Application Laid-open No. 05-291382.
In recent years, a so-called glass wafer made of quartz or the like is used in the semiconductor manufacture process in many cases. Apparatuses for detecting the slip-out of the wafer as described in Japanese Patent Application Laid-open No. 2003-273197, Japanese Patent Application Laid-open No. 2003-100852, and Japanese Patent Application Laid-open No. 05-291382 include a so-called transmission sensor for detecting the presence or absence of the wafer depending on whether or not light is blocked by the wafer. However, when the glass wafer is used, the wafer transmits the light. Therefore, even when the glass wafer is located on the optical path of the sensor, it is difficult to detect the presence of the glass wafer. In addition, even in the FIMS system connected to a film formation apparatus, it is necessary to detect not only the presence or absence of a transparent wafer before film formation but also the presence or absence of an opaque wafer after the film formation without any change.